This invention relates to coordinate positioning apparatus. A typical application of the invention is in three-dimensional measuring machines i.e. in coordinate positioning apparatus adapted for determining the spatial measurement, in three dimensions, of workpieces or other objects.
In such machines, the taking of a measurement involves moving a tool such as a surface-sensing probe into sensing relationship, e.g. into physical engagement, with a surface the position of which is to be determined. Readings of the position in space of the movable parts of the machine relative to the fixed parts are then taken, e.g. from measuring devices such as scales. There are machines where the probe is moved automatically, at desirably high speeds, from one surface to the next of a workpiece to be measured. At each surface the probe has to be decelerated when approaching the surface and accelerated when being withdrawn from the surface to be moved to the next surface. The economy of measuring complex workpieces depends on the speed at which the machine can be operated.
However, in conventional measuring machines the movable components, especially the movable bridges found in such machines, are relatively massive because of the need for stability of measurement. Less massive components would tend to be less stiff, and would suffer dynamic deflections when accelerated and decelerated. Such components require large forces for acceleration and heavy foundations to provide reaction. Therefore, such machines are intrinsically not suitable for high speed operation; there is a conflict between speed and stability of measurement.